d09 p1 (slow)

2018/09-test.txt

@@ -0,0 +1 @@
+10 players; last marble is worth 1618 points

2018/09.rkt

@@ -0,0 +1,30 @@
+#lang debug br
+(require racket/file)
+
+(define (★)
+  (match-define (list player-count marble-count)
+    (map string->number (regexp-match* #px"\\d+" (file->string "09.txt"))))
+  (define scores (make-hasheqv))
+  (let loop ([marble 1] [pos 0] [circle (list 0)])     
+    (cond
+      [(> marble marble-count) (argmax cdr (hash->list scores))]
+      [(zero? (modulo marble 23))
+       (define len (length circle))
+       (define deletion-pos (modulo (+ (- pos 7) len) len))
+       (define-values (head tail) (split-at circle deletion-pos))
+       (define player (modulo marble player-count))
+       (hash-update! scores player (λ (sc) (+ marble (car tail) sc)) 0)
+       (loop (add1 marble) deletion-pos (append head (cdr tail)))]
+      [else
+       (define next-pos (add1 (modulo (add1 pos) (length circle))))
+       (define-values (head tail) (split-at circle next-pos))
+       (loop (add1 marble) next-pos (append head (list marble) tail))])))
+
+#;(define (★★)
+    )
+#;(★★)
+
+#;(module+ test
+    (require rackunit)
+    (check-equal? (time (★)) 437654)
+    (check-equal? (time (★★)) 566))

2018/09.txt

@@ -0,0 +1 @@
+400 players; last marble is worth 71864 points